A manufacture of paper typically comprises steps of preparing paper stock, making a paper web, coating the paper web with an appropriate coating color, and finishing the paper web. In the process of preparing the paper stock, a pulp is extracted from wood or other fiber plant by chemical or mechanical treatment. In particular, in order to obtain the pulp, wood or other fiber plant is supplied to a barker so as to peel. Subsequently, the peeled wood or other fiber plant is transferred to a grinder, in which the wood or other fiber plant is mixed with water and ground in the form of slurry. Finally, the pulp for papermaking is prepared by screening the slurry.
On the other hand, the paper stock may be obtained from other materials such as a chemical pulp or a DIP (De-Inking pulp). The paper stock sequentially goes through several basic processes such as papermaking, coating and finalizing, and other additional processes subject to special requirements, thereby being formed into a web of paper wound around a roller.
In detail, the papermaking process is divided into an injecting process for uniformly injecting the paper stock, a distributing process for leveling the injected paper stock, a pressing process for pressing and dewatering the paper stock by means of a press roll, a pre-drying process for firstly drying the paper stock in the form of a web, an after-drying process for balancing the moisture contained in the web of paper, a leveling process for adjusting the thickness and smoothness of the paper web by using a pressing roll, and a winding process for winding the paper web around a roller.
The coating process, in which a paper web is coated with an appropriate coating color by a coater, specifically comprises processes of unwinding the paper web from the roller, applying a coating color (pigments, binders and additives) to the surface of the paper web in order to provide therewith smoothness or gloss, drying the paper web coated with the composition by means of steam or hot air, and re-winding the paper web around the roller.
A conventional coater employed in the above coating process will be explained in detail below with reference to the accompanying FIGS. 7 and 8.
The coater includes a backing roll 20 that transfers paper web 10 to be coated while supporting the paper web 10. Disposed adjacent to the lower end of the backing roll 20 is a nozzle 18 for injecting coating color 12 to the surface of the paper web 10. The coater further comprises a coating blade 14 which applies the coating color 12 to the paper web 10 in an evenly distributed manner. The coating blade 14 is configured to be biased against the surface of the backing roll 20. In addition, the coater is provided with a profile tube 16 positioned at the outer side of the coating blade 14 for configuring the profile of the coating blade 14 and a base 22 on which the profile tube 16 is mounted.
The width of the coating blade 14 is substantially the same with the width of the backing roll 20, whereby the coating blade 14 enables to doctor the surface of the paper web 10 in a time, over which the injected coating color 12 is disposed.
As shown in FIG. 7, the paper web 10 is continuously transferred via the rotation of the backing roll 20 while tightly partially contacting to the surface of the backing roll 20. To the surface of the paper web 10 a nozzle 18 injects a coating color 12 and the coating blade 14 evenly distributes and applies the coating color 12 over the surface of the paper web 10. During the application of the coating color 12 on the paper web 10, the excess of the coating color 12 is removed by the coating blade 14. Such a process is called as a metering process. (see the attached FIG. 8)
The metering process can be adjusted by shifting the position of the coating blade 14, which can be conducted by controlling a cylinder built in the profile tube 16 so that the desired amount of the coating color can be applied to the paper web 10. In order to collect the excess of the coating color removed during metering process, a collecting means 40 is furnished below the nozzle 18.
However, such a conventional coater has disadvantages as follows.
Referring to FIG. 7, some of the coating color 12 is accumulated at the distal end of the coating blade 14 due to the increase of the density thereof while passing between the coating blade 14 and the paper web. The accumulated coating color becomes bigger and ultimately forms a stalagmite that leads to occurrence of scratches on the paper web and transference of the stalagmite to the paper web.
In particular, at high speeds of the paper web the density of the coating color instantaneously increases passing through the coating blade due to high shear stress applied thereon and abrupt dewatering by a pressure, which results in occurrence of bleeding or streaking at the distal end of the coating blade. Such an accumulation of the coating color ultimately forms a stalagmite leading to imperfection of coated paper.
In this regard, U.S. Pat. No. 5,219,618 (Jun. 15, 1993) discloses a device that prevents a formation of a stalagmite by spraying fluid to the end of a blade and coating color.
Moreover, Japanese unexamined patent publication No. H4-228700 (Aug. 18, 1992) also discloses a device capable of inhibiting the formation of a stalagmite, wherein an injecting means are provided so as to spray fluid to a boundary area between paper web and the downstream of the coating blade. The above-described prior arts are characterized in preventing a formation of the stalagmite by providing a spraying means of fluid.
Under this circumstance, it has been strongly demanded to provide a paper coating device and system capable of effectively preventing the increase of the density of coating color while maintaining moisture. Further, it has been demanded to provide a paper coating device and system capable of significantly reducing a bleeding and streaking phenomena during a paper coating operation, thereby improving productivity and quality of coated paper.